A Pluto-Charon Sonata. III. Growth of Charon from a Circum-Pluto Ring of Debris

A Pluto-Charon Sonata. III. Growth of Charon from a Circum-Pluto Ring of DebrisKenyon, Scott J.Bromley, Benjamin C.DOI: info:10.3847/1538-3881/ab38b7v. 158142
Kenyon, Scott J. and Bromley, Benjamin C. 2019. "A Pluto-Charon Sonata. III. Growth of Charon from a Circum-Pluto Ring of Debris." The Astronomical Journal 158:142. https://doi.org/10.3847/1538-3881/ab38b7
ID: 154624
Type: article
Authors: Kenyon, Scott J.; Bromley, Benjamin C.
Abstract: Current theory considers two options for the formation of the Pluto-Charon binary. In the hit-and-run model, a lower mass projectile barely hits the more massive Pluto, kicks up some debris, and remains bound to Pluto. In a graze-and-merge scenario, the projectile ejects substantial debris as it merges with Pluto. To investigate the graze-and-merge idea in more detail, we consider the growth of Charon-mass objects within a circum-Pluto ring of solids. Numerical calculations demonstrate that Charon analogs form rapidly within a swarm of planetesimals with initial radii r 0 ≈ 145-230 km. On timescales of ̃30-100 days, newly formed Charon analogs have semimajor axes, a ≈ 5-6 r P , and orbital eccentricities, e ≈ 0.1-0.3, similar to Charon analogs that remain bound after hit-and-run collisions with Pluto. Although the early growth of Charon analogs generates rings of small particles at a ≈ 50-275 r P , ejection of several 145-230 km leftovers by the central Pluto-Charon binary removes these small solids in 10-100 yr. Simple estimates suggest that small particles might survive the passage of 10-20 km objects ejected by the central binary. Our results indicate that the Pluto-Charon circumbinary satellite system was not formed by a graze-and-merge impact when the formation of Charon within a circum- Pluto disk leads to the ejection of several 100-200 km particles through the orbital plane of the Pluto-Charon binary. If a growing Charon ejects only much smaller particles, however, graze-and-merge impacts are a plausible formation channel for the Pluto-Charon binary and an ensemble of small, circumbinary satellites.